In the years prior to Alexander's birth his father had worked as a railway labourer and the family appear on the 1881 census living at Old Toll House in Rescobie, Forfarshire. Alexander first appears on the 1891 census when he and his family are residing at Cottar House in Littleton, Longforgan, Perthshire. When the 1901 census was conducted the family were residents of Seggieden Porter Lodge in Kinfauns, his father now working as an estate labourer, but Alexander was not present at his whereabouts at the time are unknown.

He and his brothers James and William later emigrated around 1905 and settled in Philadelphia where they worked as Lace weavers, showing up on the 1910 census as boarders at 2918 Sixth Street. Exactly when Cairns came into the employ of William Ernest Carter is not known.

Cairns boarded the Titanic at Southampton as a first class passenger, travelling in the Carter entourage and on the same ticket as Augusta Serreplaà, the Carters' French maid (ticket number 113798 which cost £31). Whilst aboard he occupied cabin B86.

Alexander lost his life in the sinking and his body, if recovered, was never identified.

His parents later benefited from the Titanic Relief Fund1; he is commemorated on the family grave in Kinfauns:

THEIR BROTHER ALEXANDER

BORN AT KINFAUNS, 19TH APRIL 1883

LOST WITH "TITANIC," 15TH APRIL 1912

His mother later died in 1920 and his father in 1926 whilst several of his siblings later emigrated and settled in Australia. His brother Andrew died in Sydney in 1934 and his brother James in Queensland in 1935.